1. Field of the Invention
Although the teaching of this invention may be used for a battery charger for a variety of storage batteries, it is specifically directed toward use with motive power batteries such as those used in riding lawn mowers, garden tractors, golf carts and other electrically driven vehicles. The batteries in vehicles of this nature ordinarily can only be used for a relatively short period of time and then must be recharged to get them ready for the next period of use. Typical is the case of an electric golf cart in which the battery can be used for one or possibly two rounds of golf and then must be recharged, generally overnight, to get ready for use on the next day. This must continue day after day throughout the golf season in order to keep the cart in use. However, even after the golf season, when the carts are not in daily use, it is advisable to periodically give the batteries some amount of charge to prevent them from self-discharging in storage.
2. Description of the Prior Art
Although storage batteries have been popularly used for a long period of time, there are still a number of problems that are encountered in trying to keep them in good working condition by charging. The following are some of the factors responsible for the problems. For one, after a battery has been in use for awhile and has undergone a number of recharges, it may still be useful but its characteristics will be significantly different from its characteristics when it was new. Another factor is that the battery characteristics are significantly different under different environmental conditions and particularly at different temperatures. Still another factor is that ordinary storage batteries and chargers, such as those used for electrically powered vehicles as the present invention is principally concerned with are used under all kinds of conditions and environments so that the battery chargers necessary to keep the vehicles in operation should be rugged and simple.
On the one hand, it is often desirable to charge a battery with a fairly heavy charging current in order to speed up the charging rate. This may, and often does, result in severe overcharge with resulting damage to the battery in the form of corrosion of the plates and excessive gassing which loosens active material. It could also lead to elevated temperatures in the battery which can be damaging to the battery structure. On the other hand, a charging current that is too low may and often does result in the battery being undercharged and therefore the cells have a tendency to lose capacity.
To overcome the conflict between charging at too high of a rate and charging at too low of a rate, there has been developed a number of battery chargers incorporating quite elaborate control circuits for continually monitoring the charge status of a battery under charge and varying the charging current accordingly. These types of battery chargers generally have to incorporate sophisticated and highly complex electronic circuitry. Not only are they costly, but are also not favored by the user because of their complexity. The present invention provides a simple yet rugged battery charger for a storage battery used in electric vehicles which will automtically provide the finish charging current in the desired narrow range, regardless of the age of the battery or the temperature at which it is being charged.